1. Field
The following description relates to a bulk acoustic wave resonator and a filter including the same.
2. Description of Related Art
In accordance with a rapid increase in development of mobile communications devices, chemical devices, and biological devices the demand for compact and lightweight filters, oscillators, resonant elements, acoustic resonant mass sensors, and other elements has also increased.
As a means for implementing the compact and lightweight filters, oscillators, resonant elements, and acoustic resonant mass sensors, a film bulk acoustic resonator (hereinafter referred to as “FBAR”) is well known in the art. The FBAR has an advantage in that it may be mass produced at a minimal cost and may be subminiaturized. Further, the FBAR has advantages in that it allows a high quality factor Q value, which is a main property of a filter. Further, the FBAR may even be used in a micro-frequency band, and operate at bands of a personal communications system (PCS) and a digital cordless system (DCS). Generally, the FBAR has a structure including a resonating part formed by sequentially laminating a first electrode, a piezoelectric layer, and a second electrode on a substrate.
An operation principle of the FBAR will be described below. First, when an electric field is induced in the piezoelectric layer by applying electric energy to the first and second electrodes, the electric field causes a piezoelectric phenomenon of the piezoelectric layer, thereby causing the resonating part to vibrate in a predetermined direction. As a result, a bulk acoustic wave is generated in the same direction as the vibration direction of the resonating part, thereby causing resonance.